Streptococcus pneumoniae (Pnc) is the leading vaccine preventable cause of serious infection in infants. The current Pnc conjugate vaccines are safe, immunogenic, and effective. However, the vaccine is very expensive (approximately USD $200/infant) so it is unlikely to be affordable for most developing countries. Moreover, as health care access in developing countries may be episodic and unreliable, many children do not receive either complete or timely vaccine courses. Therefore, it is important to investigate affordable and flexible ways to deliver this vaccine, which are safe and effective. A recent World Health Organization (WHO) / Global Alliance for Vaccines and Immunization (GAVI) meeting to address impediments to the introduction of these vaccines in developing countries recognized the need to evaluate other regimens of Pnc conjugate vaccine as an important research priority. This study has been deliberately formulated with that need in mind. The proposed site for this research is Fiji. Although health services are good, Pnc disease, particularly pneumonia, remains the commonest cause of childhood morbidity and mortality. Fiji has good vaccine coverage and was the first Pacific country to introduce Hib vaccine. The arrival of the new, expensive Pnc conjugate vaccine presents a dilemma for Fiji and many similar countries. The expense of this vaccine if used in the recommended 3 or 4-dose schedule would consume a large portion of the health budget. This study has two components, aimed at addressing these two issues:1. A phase 2 immunogenicity study (involving 750 infants) to evaluate regimens using reduced numbers of doses of Pnc conjugate vaccine, and using timing of dosing and combinations with polysaccharide (PS) vaccine that may be more suited to the epidemiology of Pnc disease in developing countries.2. An epidemiological study will measure the burden of invasive Pnc disease, pneumonia, and otitis media (OM) in Fiji. This will be part of a global effort to address these issues, and will be used to develop rapid assessment tools for these diseases in developing countries.